在 2022/2/21 下午7:23, Xuan Zhuo 写道:
On Mon, 21 Feb 2022 11:32:52 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
On Fri, Feb 18, 2022 at 5:00 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
On Thu, 17 Feb 2022 15:19:44 +0800, Jason Wang <jasowang@xxxxxxxxxx> wrote:
On Thu, Feb 10, 2022 at 4:51 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
virtqueue_add() only supports virtual addresses, dma is completed in
virtqueue_add().
In some scenarios (such as the AF_XDP scenario), DMA is completed in advance, so
it is necessary for us to support passing the DMA address to virtqueue_add().
I'd suggest rename this feature as "unmanaged DMA".
OK
Record this predma information in extra->flags, which can be skipped when
executing dma unmap.
Question still, can we use per-virtqueue flag instead of per
descriptor flag? If my memory is correct, the answer is yes in the
discussion for the previous version.
Yes.
per-virtqueue? I guess it should be per-submit.
This patch set only adds a flag to desc_extra[head].flags, so that we can know
if we need to unmap dma when we detach.
I meant if we can manage to make it per virtqueue, there's no need to
maintain per buffer flag.
Rethinking this question, I feel there is no essential difference between per
virtqueue and per sgs.
per virtqueue:
1. add buf:
a. check vq->premapped for map every sg
2. detach:
a. check vq->premaped for unmap
per sgs:
1. add buf:
a. check function parameter "premapped" for map every sg
b. add flag to extra[head].flag
2. detach:
a: check extra[head].flag for unmap
Thanks.
Per-virtqueue is still a little bit easier at the first glance.
Actually, per-sg have one advantage: it can be used without virtqueue
reset (to allow switching between the two modes). But I'm not sure
whether we had such requirements.
I think to answer this question, we probably need a real use case (if we
can come up with a case that is more lightweight than AF_XDP, that would
be even better).
Thanks
So we know something that needs to be mapped by virtio core itself,
e.g the indirect page. Other than this, all the rest could be
pre-mapped.
For vnet header, it could be mapped by virtio-net which could be still
treated as pre mapped DMA since it's not the virtio ring code.
Anything I miss here?
Thanks
Thanks.
Thanks
v1:
1. All sgs requested at one time are required to be unified PREDMA, and several
of them are not supported to be PREDMA
2. virtio_dma_map() is removed from this patch set and will be submitted
together with the next time AF_XDP supports virtio dma
3. Added patch #2 #3 to remove the check for flags when performing unmap
indirect desc
Xuan Zhuo (6):
virtio: rename vring_unmap_state_packed() to
vring_unmap_extra_packed()
virtio: remove flags check for unmap split indirect desc
virtio: remove flags check for unmap packed indirect desc
virtio: virtqueue_add() support predma
virtio: split: virtqueue_add_split() support dma address
virtio: packed: virtqueue_add_packed() support dma address
drivers/virtio/virtio_ring.c | 199 ++++++++++++++++++++++-------------
1 file changed, 126 insertions(+), 73 deletions(-)
--
2.31.0
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